I've got a new crab pattern that you can use for tarpon (4/0 hook), redfish (#4) and bones #6. Obviously, you've gotta vary the hackle size, dubbing amounts, etc. But:

Tie in two long strands of black krystal flash at the bend of the hook for antennae.

Tie in one tannish hen saddle feather on either side of the shank, splayed outward.

Tie in a bit of "flash" between the "claws"--I use a bit of rust or copper, and maybe some pearl k-flash, or gold, or rwinbow, or whatever bits happen to be laying on my tying bench from the last fly.

Tie in longish eyes made of burned mono. Or lead dumb-bells if you want it on the bottom fast (I vary from mono to bead-chain to lead depending upon water depth, bottom grasses, etc--and how fast I want the fly to sink).

Tie in a really webby grey hackle and "wait".

Make a "dubbing loop" and create a "spiky" body (tan, or olive) that's fairly thick.

Wind the webby (schlaapen????) hackle toward the eye of the hook. Leave the very tip of the hackle sticking out over the eye of the fly like a little "tail" and tie off. Trim the hackle top and bottom so the crab has a flat profile.